Casters are well known in the furniture art and comprise wheels mounted for rotation about a generally horizontal axis, and for swiveling about a generally vertical axis. Casters are generally used in connection with furniture that is to be moved about, and are particularly prevelant in office furniture and computer furniture. Caster wheels may be made of metal with rubber tires, or of plastic with rubber tires, or they may be all plastic. In many instances hollow plastic wheels are used in twin pairs with mounting structure intervening between the twin wheels.
The wheels must be free to turn about their axles for movement of the furniture from one place to another, but in many instances it is necessary to brake the caster wheels to maintain the furniture fixed in a given location. Various structures are known for braking caster wheels, and U.S. Pat. Nos. 3,914,821; 4,035,864; and 4,077,087 are mentioned as exemplary. In the first of the foregoing patents a shaft having a cam thereon is rotated to press a brake shoe against the inner surface of the caster wheels which comprise cup-shaped rollers, and which are adapted to be deformed when in locked or braked position. The wheel or roller must be made of resiliently deformable plastic material.
The second of the foregoing patents discloses a structure in which an over center mechanism or link operates against a resilient spring. However, the braking structure operates on the exterior of the caster wheel. The third of the foregoing patents shows links for operation of a brake shoe which presses against the exterior of the caster wheel.
In addition to the foregoing there have previously been twin wheel caster brakes which rely on a pin dropping in between pointed fins or ribs inside the rim of the wheels to prevent rotation. This requires special wheels, and may also develop a condition in which the locking pin jams against the tip of a wheel rib and does not engage properly.